Subject:
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Re: !!! Laser attachments for Mindstorms !!!
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 9 Oct 1999 04:03:38 GMT
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Viewed:
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788 times
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In lugnet.robotics, Joel Shafer writes:
> Maybe the robot could use the laser to draw spiro-graph designs on the
> wall, I'm not sure if the motors could position the beam that fast though.
I was actually working on something like this using one of those cheap little
$8 laser pointers. The idea is to use a pair of mirrors that can be rotated to
specific angular locations to build an X-Y Laser Plotter. One mirror rotates
horizontally, the other vertically. If the beam is aligned to bounce off of
both mirrors, it can be diverted to a particular (x, y) location on a screen or
wall.
I was inspired to do this by something that I saw in the LegoPitscoDactaCatalog
that did the spirograph-- I mean lissajous pattern thing. That design also
used two mirrors, but each mirror is simply mounted directly onto a motor's
drive shaft at a 45-degree angle. By varying the speed of the two motors, you
can create an infinite variety of dazzling visual effects. This would be
easier to do in Lego since you don't have to fine-position the motors at a high
speed; you simply run them at varying speeds. You can get away with almost
any old slop and you'll still get a reasonable pattern out of the thing. But
then again, the RCX motor speed doesn't seem to vary much under a low load, so
this might not work so well after all.
Anyway, I didn't get very far in actually building my X-Y Laser Plotter before
I ran into a number of challenges:
1. The geometry is tricky. I didn't have the patience to get both axes built
out of Lego, and I didn't have suitable optical-grade mirrors handy to epoxy
onto a couple of bricks.
2. Low power lasers are not great when it comes to fast scanning. If you
sweep the pointer quickly across a screen you don't really get much of a
residual trace. High-power lasers that will leave a trace are large and bulky
and can burn holes in metal (and plastic!) and vaporize small rocks.
3. I anticipate that the RCX will be a wee bit sluggish to meet the speed
requirements for this kind of control. (At least using standard firmware.) I
have no hard evidence to back this up yet, though. <See challenge #1>
4. Gear lash will kill you. I found it necessary to use a lot of gearing to
get very fine mirror angle control, and every gear adds that extra bit of error
when you reverse direction. It is possible to compensate for gear lash, but it
takes time to overcome, and affects the shape of the images that you can draw
at any speed.
5. My el-cheapo laser pointer was going to have to be modified in order to be
able to turn it on and off from the RCX. (I also considered using a third
motor to simply gate the laser beam by blocking it with a black brick, but that
was never going to be fast enough.) It sounds like Josh's new laser module has
been modified to enable the laser to be switched directly from a motor output,
which would solve this problem nicely. <Josh: Does your laser module still
contains its own batteries, or is it powered completely off of the motor output
driver?>
6. The ever-present "you'll poke your eye out with that thing!" factor.
Lasers are dangerous. Even a low-power laser pointer can cause damage to your
eyes. Be extremely careful about exposing yourself or others to eye injury!!!
But man, are they fun to play with! My cat loves them too!
Wow. A laser module for the RCX. What's next? A microwave dish?? A jet
engine?!? No, wait -- a nuclear reactor!!!
Do we live in great times, or what?
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Message has 2 Replies:
 | | RE: !!! Laser attachments for Mindstorms !!!
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| (...) SNIP (...) SNIP Big rocks, too. :>) The problem is not so much the laser, as it is your scanning. Unless you are projecting against a phorescent screen, there is no "residual" trace, regardless of power. It is the speed at which the eye can't (...) (25 years ago, 9-Oct-99, to lugnet.robotics)
| | | Re: !!! Laser attachments for Mindstorms !!!
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| One of the early things I did with my laser pen was rubberband one of the 5 stud long "helicopter rotor" plates to the side of it. I never got it balanced *perfectly*, but it was close. I then stuck the axle from the older 9 volt technic motor (...) (25 years ago, 9-Oct-99, to lugnet.robotics)
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